The provided compiler '/usr/bin/gcc' is LLVM based, it is not yet fully supported by ruby and gems, please read `rvm requirements`.

La solución luego de pasar por tantas webs fue:

https://github.com/kennethreitz/osx-gcc-installer

OSX GCC Installer

Downloading and installing the massive Xcode installer is a huge hassle if you just want GCC and related tools.

The osx-gcc-installer allows you to install the essential compilers from either pre-built binary packages or helps you create your own installer.

For Lion and Mountain Lion users, Apple now provides an official Command Line Tools for Xcode package that you can install without needing to install Xcode itself! You can download it from Apple's developer site. If you still need gcc-4.2, and you use Homebrew, you can install it using the apple-gcc42 package from homebrew/dupes.